From: Peter Xu <peterx@xxxxxxxxxx> Subject: mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte Patch series "mm: A few cleanup patches around zap, shmem and uffd", v4. IMHO all of them are very nice cleanups to existing code already, they're all small and self-contained. They'll be needed by uffd-wp coming series. This patch (of 4): It was conditionally done previously, as there's one shmem special case that we use SetPageDirty() instead. However that's not necessary and it should be easier and cleaner to do it unconditionally in mfill_atomic_install_pte(). The most recent discussion about this is here, where Hugh explained the history of SetPageDirty() and why it's possible that it's not required at all: https://lore.kernel.org/lkml/alpine.LSU.2.11.2104121657050.1097@eggly.anvils/ Currently mfill_atomic_install_pte() has three callers: 1. shmem_mfill_atomic_pte 2. mcopy_atomic_pte 3. mcontinue_atomic_pte After the change: case (1) should have its SetPageDirty replaced by the dirty bit on pte (so we unify them together, finally), case (2) should have no functional change at all as it has page_in_cache==false, case (3) may add a dirty bit to the pte. However since case (3) is UFFDIO_CONTINUE for shmem, it's merely 100% sure the page is dirty after all because UFFDIO_CONTINUE normally requires another process to modify the page cache and kick the faulted thread, so should not make a real difference either. This should make it much easier to follow on which case will set dirty for uffd, as we'll simply set it all now for all uffd related ioctls. Meanwhile, no special handling of SetPageDirty() if there's no need. Link: https://lkml.kernel.org/r/20210915181456.10739-1-peterx@xxxxxxxxxx Link: https://lkml.kernel.org/r/20210915181456.10739-2-peterx@xxxxxxxxxx Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Liam Howlett <liam.howlett@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Yang Shi <shy828301@xxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> Cc: Alistair Popple <apopple@xxxxxxxxxx> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 1 - mm/userfaultfd.c | 3 +-- 2 files changed, 1 insertion(+), 3 deletions(-) --- a/mm/shmem.c~mm-shmem-unconditionally-set-pte-dirty-in-mfill_atomic_install_pte +++ a/mm/shmem.c @@ -2423,7 +2423,6 @@ int shmem_mfill_atomic_pte(struct mm_str shmem_recalc_inode(inode); spin_unlock_irq(&info->lock); - SetPageDirty(page); unlock_page(page); return 0; out_delete_from_cache: --- a/mm/userfaultfd.c~mm-shmem-unconditionally-set-pte-dirty-in-mfill_atomic_install_pte +++ a/mm/userfaultfd.c @@ -69,10 +69,9 @@ int mfill_atomic_install_pte(struct mm_s pgoff_t offset, max_off; _dst_pte = mk_pte(page, dst_vma->vm_page_prot); + _dst_pte = pte_mkdirty(_dst_pte); if (page_in_cache && !vm_shared) writable = false; - if (writable || !page_in_cache) - _dst_pte = pte_mkdirty(_dst_pte); if (writable) { if (wp_copy) _dst_pte = pte_mkuffd_wp(_dst_pte); _
